The lever system of this professional coffee machine lets the barista modulate the pre-infusion manually for each delivery. When you lower the lever hot water from the boiler enters the group, wetting the coffee. The more the barista pulls the lever, the longer the pre-infusion phase. A good professional waits for the first drops of coffee to come out before lifting the lever; this means that water will have permeated all the coffee. For effective pre-infusion, the pressure of the water as it enters the group should not exceed 2 bars.